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thiourea alias thio, generally colorless prismatic crystal (25 ℃), water solubility of 14.2 9, ethanol is 4.0 g. Thiourea in the air easily deliquescence, a melting point of 180 - 182 ℃, when a transition at 150 ℃ ammonium thiocyanate. 180 ℃ decomposition. Thiourea molecule in the presence of a lone pair of electrons, can form complexes with metal ions digitized objects on a sulfur atom and a nitrogen atom, but with a bit constant is generally small. It is worth noting that, due to the sulfur atom of thiourea has a special affinity for the precious metals, it is often possible and precious metals form stable coordination compounds, which are widely used in electroplating and electroless plating precious metals. And thiourea is a good coplanarity small molecule, it is easy to be firmly adsorbed on the metal surface, thereby changing the metal surface electronic structure, the nature of it in the field of electroplating additive widely used.

Thiourea complexing agent application

    Thiourea sulfur atom in the molecule readily Au, Ag.Zn, Cu and Pb, a metal ion to form a stable complex compound, wherein the thiourea complex compound formed is Ag + ions [Ag (H2NCSNH2) 3] +, stable Constant 13.1; and coordination compounds formed is ion Au + [Au (H2NCSNH2) 2] +, instability constant 4.2 × 10-23; and Cu + form of [Ag (H2NCSNH2) 4] ', constant instability 7.9 x 10 -16, which is widely used in the noble metal complex compound

Material, such as gold plating, electroless tin-lead alloy, powder and silver-plated nickel layer stripping and other substandard.

Thiourea used in the plating

    Cai Jiqing noted that when the surface of the Cu or Cu alloy plating Sn-Zn alloy plating solution was added thiourea and its derivatives, can significantly reduce the activity of Cu2 + in the bath, help Sri2 + substitution precipitation, but the concentration of thiourea preferably 0.3-2. O moVL. If the concentration is less than 0.3mol / L, Sn, and Zn is difficult to precipitate, since (as 137 g / L at 20 ℃) thiourea solubility limit, at a concentration not higher than 2.0 mol / L. When Lili noted tin alloy, thiourea can complex metal ions in the form of compounds stably exist, especially in the plating Sn - Ag alloy plating thiourea was added, the bath so that its coordination role in Snz + and Ag + replacement reaction between copper and copper alloys can be carried out smoothly and successfully co-deposition surface to form Sn -Ag alloy coating. To Jiang and other plating Sn-Pb alloy was found on Cu plating, thiourea and CtI + to form a stable complex compound, alter the equilibrium potential Cu and Sn, Pb, and 80 g / L concentration of thiourea is preferred .

Thiourea Application in Electroplating

    studies Icconi GI and MacagnoV A, etc. show that the silver plating process, the silver crystals growing up in the thiourea adsorbed layer, and the size and number of thiourea silver crystals in sediments content. Upadhyay DN and other studies have shown that the content of thiourea can affect Cu deposition on Au substrate.

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